1. Valery Telnov Budker INP, Novosibirsk LC-ECFA-2013, DESY, May 31 Photon collider: summary

2. LC-ECFA, 2013, DESY, 2013 Valery Telnov 2 α c ~25 mrad ω max ~0.8 E 0 W γγ, max ~ 0.8·2E 0 W γe, max ~ 0.9·2E 0 b~γσ y ~ 1 mm For the Higgs factory one needs E 0 ~105 GeV, λ~1 μm

3. LC-ECFA, 2013, DESY, 2013 Valery Telnov 3 Realistic luminosity spectra (  and  e ) ( with account multiple Compton scattering, beamstrahlung photons and beam-beam collision effects) (decomposed in two states of J z ) Usually a luminosity at the photon collider is defined as the luminosity in the high energy peak, z>0.8z m. L γγ (z>0.8z m ) ~0.1 L e-e- (geom) For ILC conditions (but cross sections in γγ are larger then in e+e- by one order!) (ILC)

4. LC-ECFA, 2013, DESY, 2013 Valery Telnov 4 The resonance Higgs production is one of the gold-plated processes for PLC γ γ (previous analyses) realistic simulation P.Niezurawski et al For M H =115-250 GeV ILC S.Soldner-Rembold (thr first simulation) At nominal luminosities the number of Higgs in γγ will be similar to that in e+e-. The effective cross section (in terms of e-e- luminosity) is about 200 fb. V.T,1999 (is considered for PLC since 1980 th ) H→bb H→ γγ

5. LC-ECFA, 2013, DESY, 2013 Valery Telnov 5 Remark on Photon collider Higgs factories Photon collider can measure Г(H→γγ)*Br(H→bb, ZZ,WW), Г 2 (H→γγ)/Г tot, CP properties (using photon polarizations). In order to get Г(H→ γγ ) one needs Br(H→bb) from e+e-. This gives also Г tot. e+e- can also measure Br (bb, cc, gg, ττ, μμ, invisible), Г tot, less backgrounds due to tagging of Z. Therefore PLC is nicely motivated in combination with e+e-: parallel work or second stage.

6. LC-ECFA, 2013, DESY, 2013 Valery Telnov 6 Physics motivation for PLC (independent on physics scenario) (shortly) In ,  e collisions compared to e + e - 1.the energy is smaller only by 10-20% 2.the number of events is similar or even higher 3.access to higher particle masses (H,A in γγ, charged and light neutral SUSY in γe) 4.higher precision for some phenomena ( Γγγ, CP-proper.) 5.different type of reactions (different dependence on theoretical parameters) It is the unique case when the same collider allows to study new physics in several types of collisions at the cost of rather small additional investments

7. LC-ECFA, 2013, DESY, 2013 Valery Telnov 7 The discovery of the Higgs have led to appearance of many projects of Higgs factories, among them about ten projects of gamma-gamma Higgs factories without e+e- :

8. LC-ECFA, 2013, DESY, 2013 Valery Telnov 8 Dec. 21, 2012, INP seminarValery Telnov 8

9. LC-ECFA, 2013, DESY, 2013 Valery Telnov 9 CERN SLAC FNAL SLAC JLABFNAL JLAB KEK (with e+e-) γγ Higgs factories appeared in 2012-2013 years

10. LC-ECFA, 2013, DESY, 2013 Valery Telnov 10 In my opinion, these projects look not serious (because without e+e-), but demonstrate the interest of physics community to photon colliders. Much more natural, realistic and physics motivated are γγ, γe colliders based on e+e- projects ILC and CLIC. Unfortunately, since 2006 GDE considered only the baseline ILC (only e+e-) without any options and at present the ILC design is incompatible with the photon collider.

11. LC-ECFA, 2013, DESY, 2013 Valery Telnov 11 It is still not too late to make necessary modifica- tions: the second IP or space for the crossing angle 25 mrad; space for the beamdump; space for a laser system. 14mr => 25mr

12. LC-ECFA, 2013, DESY, 2013 Valery Telnov 12 The ILC scope document, 2006

13. LC-ECFA, 2013, DESY, 2013 Valery Telnov 13 One of the authors of the LC scope document was Sachio Komamiya and now being the head of the LC board he has a good opportunity to bring the ILC design in agreement with the scope document requirements. It is really extremely important to make the required changes during this-next years.

14. LC-ECFA, 2013, DESY, 2013 Valery Telnov 14 The photon collider at ILC (TESLA) has been developed in detail at conceptual level, all simulated, all reported and published (TESLA TDR (2001) and updated later. The conversion region: optimization of conversion, laser scheme. The interaction region: luminosity spectra and their measure- ment, optimization of luminosity, stabilization of collisions, removal of disrupted beams, crossing angle, beam dump, backgrounds. The laser scheme (optical cavity) was considered by experts, there is no stoppers. Required laser technique is developed independently for many other applications based on Compton scattering. Recently LLNL started work on LIFE lasers for thermonuclear plant which seems very attractive (one pass laser). Further developments need political decisions and finances.

15. LC-ECFA, 2013, DESY, 2013 Valery Telnov 15 2001 10-15 years ago PLC community accounted >100 active people, we had several special PLC workshop. Now the interest to PLC is not smaller but activity is much reduced (in the stand by mode) due to unmotivated exclusion (in 2006) of the PLC from the ILC project.

16. LC-ECFA, 2013, DESY, 2013 Valery Telnov 16 Requirements for laser Wavelength ~1 μm (good for 2E<0.8 TeV) Time structure Δct~100 m, 3000 bunch/train, 5 Hz Flash energy ~5-10 J Pulse length ~1-2 ps

17. LC-ECFA, 2013, DESY, 2013 Valery Telnov 17 Laser system The cavity includes adaptive mirrors and diagnostics. Optimum angular divergence of the laser beam is ±30 mrad, A≈9 J (k=1), σ t ≈ 1.3 ps, σ x,L ~7 μm

18. LC-ECFA, 2013, DESY, 2013 Valery Telnov 18 4 mirror cavities are at the ATF KEK-Hiroshima installed 2011 LAL-Orsay installed summer 2010 relatively simple control system employs new feed back scheme sophisticated control digital PDH feedback So far –2.6kW stored w/ enhancement of 1230 –Highly stable ΔL ～ 4pm –vertical laser size at the IP 13  m –120g/5bunches -> ~2.6×10 8 /sec –Digital Feedback Quantitative understanding –Finesse –Powers –Profile H. Takahashi

19. LC-ECFA, 2013, DESY, 2013 Valery Telnov 19 16 Hz, 8.125 kJ/pulse, 130 kW aver. power Project LIFE, LLNL Recently new option has appeared, one pass laser system, based on new laser ignition thermonuclear facility (the pulse can be split into the ILC train) So, the required lasers almost exist.

20. LC-ECFA, 2013, DESY, 2013 Valery Telnov 20 Laser diodes cost go down at mass production, that makes one pass laser system for PLC at ILC and CLIC realistic!

21. LC-ECFA, 2013, DESY, 2013 Valery Telnov 21 Fiber Lasers Gerard Mourou et al., “The future is fiber accelerators,” Nature Photonics, vol 7, p.258 (April 2013). ICAN – International Coherent Amplification Network 10 J, 10 kHz

22. LC-ECFA, 2013, DESY, 2013 Valery Telnov 22 Some dreams of γγ factories at ILC (PLC based on ILC, with very low emittances, without damping rings)

23. LC-ECFA, 2013, DESY, 2013 Valery Telnov 23 Factors limiting γγ,γe luminosities So, one needs: ε nx, ε ny as small as possible and β x, β y ~ σ z Collision effects: Coherent pair creation ( γγ) Beamstrahlung ( γe) Beam-beam repulsion ( γe) On the right figure: the dependence of γγ and γe luminosities in the high energy peak vs the horizontal beam size (σ y is fixed). At the ILC nominal parameters of electron beams σ x ~ 300 nm is available at 2E 0 =500 GeV, but PLC can work even with ten times smaller horizontal beam size. Telnov,1998 (ILC) In γγ collsions the luminosity is limited only by available beam sizes or geometric e - e - luminosity (for at 2E 0 <1 TeV).

24. LC-ECFA, 2013, DESY, 2013 Valery Telnov 24 Method based on longitudinal emittances V.Telnov, LWLC10, CERN Let us compare longitudinal emittances needed for ILC with those in RF guns. At the ILC σ E /E~0.3% at the IP (needed for focusing to the IP), the bunch length σ z ~0.03 cm, E min ~75 GeV that gives the required normalized emittance ε nz  (σ E /mc 2 )σ z ~15 cm In RF guns σ z ~0.1 cm (example) and σ E ~ 10 keV, that gives ε nz ~2·10 -3 cm, or 7500 times smaller than required for ILC! So, photoguns have much smaller longitudinal emittances than it is needed for linear collider (both e+e- or γγ). How can we use this fact ?

25. LC-ECFA, 2013, DESY, 2013 Valery Telnov 25 Let us combine many low charge, low emittance beams from photo-guns to one bunch using some differences in their energies. The longitudinal emittance increases approximately proportionally to the number of combined bunches while the transverse emittance (which is most important) remains almost constant. A proposed method It is assumed that at the ILC initial micro bunches with small emittances are produced as trains by one photo gun.

26. LC-ECFA, 2013, DESY, 2013 Valery Telnov 26 Scheme of combining one bunch from the bunch train (for ILC) (64→1)

27. LC-ECFA, 2013, DESY, 2013 Valery Telnov 27 Beam parameters: N=2·10 10 (Q~3 nC), σ z =0.4 mm Damping rings(RDR): ε nx =10 -3 cm, ε ny =3.6·10 -6 cm, β x =0.4 cm, β y =0.04 cm, RF-gun (Q=3/64 nC) ε nx ~10 -4 cm, ε ny =10 -6 cm, β x =0.1 cm, β y =0.04 cm, The ratio of geometric luminosities L RFgun /L DR =~5-10 Hopes So, with polarized RF-guns one can get the luminosity ~5-10 times higher than with DR. Polarized RF-guns still have emittances larger than that of unpolarized guns but there is good progress and soon we will have the required low emittance polarized guns.

28. LC-ECFA, 2013, DESY, 2013 Valery Telnov 28 Conclusion Photon colliders is a very cost effective addition for e+e- linear colliders: as the LC second stage or as the second IP (preferable). All required technologies exist. The ILC is close to approval. It is very important to make the final ILC design compatible with the photon collider and further develop the PLC as an integral part of the ILC project.